In certain engine applications such as in aircraft turbine engines, fuel is ignited by an igniter of the surface gap type. In a high voltage igniter of the surface gap type and in a surface gap spark plug, the spark travels along the surface of a ceramic insulator between a center electrode and an annular ground electrode which surrounds the center electrode. In a low voltage igniter, the spark travels along a semiconductor surface located between the center electrode and the surrounding ground electrode. In either type of igniter, the ground electrode is subject to spark erosion during use. A special tool or gauge is required to inspect and check for wear on the ground electrode. For the low voltage igniter, the semiconductor surface also is subject to wear during use. As the semiconductor surface wears, an increasing portion of the center electrode is exposed.
It is often difficult for a mechanic to tell when an igniter is sufficiently worn to require replacement. Since igniters are expensive, premature replacement should be avoided. However, failure to replace a worn out igniter could lead to catastrophic results if the igniter is used, for example, in an aircraft engine.